1. Field of the Invention
The present invention relates to a supervisory apparatus for transmission lines in a terminal office transmitting and receiving an optical signal and an optical amplifying and repeating apparatus or other optical communication apparatus used in an optical transmission system performing optical communication.
2. Description of the Related Art
One of the methods of detecting the status of optical communication apparatuses in transmission lines is to add the times at the apparatuses when transmitting information on faults occurring in the optical communication apparatuses.
In this method, an optical communication apparatus writes fault information in a supervisory frame when receiving that fault information and manages the times written in the frames for the sender apparatuses.
It compares the time written in a frame,describing fault information and the times of sender apparatuses which itself manages and discards the frame when the time in the frame is smaller than or equal to the times of the sender apparatuses.
That is, each apparatus has a fixed area for managing the times in the frames to judge if a frame has already been received.
To reset the above fault information, a fixed information region is added to a frame carrying the reset information for resetting the fault information. An optical communication apparatus receiving the reset frame avoids recirculation of the frame by adding to the information region information showing the completion of reception.
Summarizing the problems to be solved by the invention, in the past, the operation for discarding a frame describing fault information has been managed by time. Therefore, when the time at the optical communication apparatus changes, it is necessary to send a reset frame to update the time managed by the optical communication apparatus in the network.
Further, since it was necessary to match with the time in the network, the time had to be matched in the system in the network frequently. In this case, the frequent transmission of frames carrying reset information for all apparatuses resetting fault information at one time becomes a cause of line congestion.
In the information region fixedly defined in the reset frame, since there is a one-to-one correspondence between the information storage positions and number of the optical communication apparatus, it is necessary to enlarge the information region when giving optical communication apparatuses large numbers. Further, in a system not setting consecutive numbers for the optical communication apparatuses, unnecessary information is added.
An object of the present invention, in view of the above problems, is to eliminate the need for management of the times of supervisory apparatuses in a network.
Another object of the present invention is to simply prevent recirculation of frames.
A further object of the present invention is to enable, at all times, just the minimum necessary region to be held as the information region in a reset frame.
To attain the above objects, according to the present invention, there is provided a supervisory apparatus for supervising an optical communication apparatus connected to transmission lines, which supervisory apparatus add a sequence number when sending a supervisory frame.